1. Field of the Invention
The present invention relates an occupant detection sensor for detecting whether an occupant sits on a seat. The present invention also relates to a method of manufacturing an occupant detection sensor.
2. Description of the Related Art
JP-A-2005-233845 discloses a film sensor disposed in a narrow space between two rows of hanging grooves. In the film sensor, a sensor side end is located on a virtual substantially linear band that connects outside of a pair of sensor cells located closest to the sensor side end so as to secure occupant detection accuracy.
The narrow space in which the film sensor is disposed is located at a portion corresponding to a buttock of an occupant. Thus, the film sensor can detect sitting at a buttock but cannot detect sitting at a thigh. For example, even when a child stands in the vicinity of a backrest of a vehicle seat, the film sensor may be subjected to a load and may detect sitting of an occupant by error.
In some cases, the number of hanging grooves provided on a surface (upper side) of a cushion pad in a vehicle seat is increased to improve design or comfortableness. If the above-described film sensor is applied to such a seat without changing a shape, a coupling section (that is, a portion between sensors or a portion between a sensor and a connector) may straddle the hanging groove. A seat cover that covers the cushion pad includes a portion (trench portion) put in the hanging groove. When the seat cover is attached, the trench portion pushes the coupling section into the hanging groove. Then, the coupling section located at an edge of the hanging groove is bent and stress is generated. The stress influences the sensors through the film.
The sensor subjected to the stress is curved in accordance with the stress, and a distance between carbon layers increases. In other words, because the film sensor cannot detect sitting of an occupant unless the film sensor is subjected to a load greater than a sensor that is not subjected to a stress, accuracy (sensitivity) is reduced. Furthermore, because the sensor is continuously pressed down by the seat cover, the sensor may be damaged (for example, peeling off of the film or a silver layer) when a stress generated by bending exceeds a tolerance.